1. Field
The aspects of the disclosed embodiments relate to a method and a device for machining a workpiece, which can be advantageously used for producing cutting tools having diamond cutting edges, for example.
FIG. 1a and FIG. 1b shows the relationships by way of diagram. 10 denotes a workpiece. FIG. 1a shows by way of diagram and in perspective part thereof during the production while FIG. 1b is a sectional drawing. In FIG. 1b, 19 stands for a metallic basic body which is shaped in suitable fashion and as desired. It is coated with an artificially formed diamond layer which includes areas 14 and 16 between which a separating line 15 is shown. The diamond layer has been applied to the manufactured blank 19 and can be a CVD diamond layer (chemical vapor deposition) or a PKD diamond layer (polycrystalline diamond). Upon conclusion of the task, the thickness thereof is greater than required most recently and the form required most recently, including the cutting edge of the cutting tool, is produced by removing the excessive diamond material by means of a laser removal machine until the finally desired form including the cutting edge form has been obtained.
FIG. 1a shows by way of diagram and in perspective a partially manufactured cutting tool. The upper area is already fully manufactured, the edge 11 is the cutting edge of the cutting tool and has already been worked out in the machining stage as shown. It is assumed that the flanks of the cutting tool in the finally desired form still have to be produced downwardly by removing excessive diamond material. In FIG. 1b, this means that the material 14 is removed from the outside of the blank to the boundary 15, a process that is made in layers, wherein the layers are parallel to the drawing plane and are stacked perpendicularly thereto. In FIG. 1a, this is done by guiding a laser beam 13 over the accessible surface of the excessive material to liquefy and evaporate (also vapor expulsion of liquid droplets) or combust the material.
The guidance of the laser beam 13 over the accessible workpiece surface is done in strips in such a way that several lines, which lie next to one another, are traveled over sequentially so as to jointly cover a removed layer. In FIGS. 1a and 1b, these strips are designated by reference sign 51 while the layers still to be removed in future are outlined by the dashed lines 17. A layer of the material is removed by means of several strips which lie next to one another and border on one another and, and by removing several layers (in FIG. 1a stacked in the z-direction perpendicular to the drawing plane), the finally desired form of the workpiece is worked out of the blank.
FIG. 2a shows by way of diagram a laser machining machine. 10 again denotes the workpiece while 25 stands for a laser tool from which a focused, convergent laser beam 13 originates which is directed to the workpiece. 24 is a workpiece table and 23 is a machine support. 22a and 22b are translational and/or rotatory control axes by means of which relative positions (x, y, z) can be adjusted in three-dimensional fashion between tool and workpiece and by means of which alignments (phi, psi) of workpiece and tool relative to each other can also freely be adjusted. Depending on the type of machine and suitability, the control axes can be provided between machine frame 21 and the workpiece table 24 and/or between machine frame 21 and tool holder 23. Axes can be provided redundantly. It is preferred to provide at least three translational control axes and two rotatory control axes.
26 generally denotes sensors for detecting process parameters. They can also be designed for detecting the workpiece surface directly during the machining operation of the workpiece and can optionally also measure the workpiece in a three-dimensionally resolving fashion in a resolution corresponding to the finishing accuracy. 27 stands for a machine control system. It can be a digital process computer which can also be connected to a larger or smaller network. The control system is connected to a memory 28 which along with different other data also contains data which are required for generating the control signals for the laser tool 25, on the one hand, and the control axes 22, on the other hand. 29 denotes the interface between control system 27 and machine 20. It comprises, on the one hand, lines for signals and/or (switched, keyed) output and comprises in addition conversion devices (not shown) for format conversion, analog-to-digital conversion or digital-to-analog conversion and the like.
The laser tool 25 is shown in FIG. 2b. It is designed to guide the laser beam over the surface of the workpiece as desired while controlling the machine control system 27, in particular to travel over the strips 51 outlined in FIG. 1a. This can be done through controllable and adjustable mirrors 25a in a two-dimensional way. Moreover, a focusing adjustment 25b can be provided (“z-shifter”) which follows the focus position of the laser beam 13 up to the work progress (in the z-direction in FIG. 1a), on the one hand, and to the crown in the case of a laser deflection, on the other hand.
However, in the production of workpieces to be produced in highly precise fashion, such as cutting tools having a diamond coating, the optical elements 25a have not been used for the beam guidance (adjustable mirrors) to date. The mechanical control axes 22a and 22b of the machine 20 have been used instead, while the laser beam 13 originated in stationary fashion in relation to the laser tool 25 from the latter.
The beam guidance of the laser by means of adjustable mirrors 25a has the advantage that it is comparatively fast. It serves for adjusting strip guidance speeds (moving speeds of the laser impact point or spot on the workpiece surface) of over 1 m/s up to 10 m/s and more. However, the drawback of this optical beam guidance is that it is rather inaccurate dynamic-wise, in particular often more inaccurate than the required tolerances. On the contrary, the beam guidance is much more accurate but also markedly slower when the relative guidance between laser tool 25 and workpiece 10 is not made via the adjustable mirrors 25a but via the mechanical control axes 22a and 22b (translational and/or rotatory, provided between machine frame 21 and tool support 23 and/or between machine frame 21 and workpiece table 24). In this case, accuracies of up to some few micrometers are possible. However, the achievable speeds are markedly slower in the case of a mechanical guidance. They are usually below 10 mm/s (strip guidance speed of the laser impact point on the workpiece surface). They are thus usually below those achievable with an optical beam guidance by a factor of at least 100, and therefore the production of workpieces are markedly prolonged.
2. Brief Description of Related Developments
In certain workpieces, e.g. cutting tools, a high degree of accuracy of the finished geometry is desirable, and therefore when the workpiece is produced by means of a laser, the use of the mechanical control axes 22a instead of the optical elements 25a is necessary for the laser beam guidance to achieve the desired accuracies. The comparatively slow and therefore long lasting operation is less disturbing when there is comparatively little overall material to be removed. In the case of cutting tools equipped with diamonds this is e.g. the case when the diamond coating consists of CVD diamonds since the thus produced coatings of the blank are comparatively thin and only have small protruding amounts of material, and therefore only relatively small volumes have to be removed.
However, it has turned out that is also desirable to produce workpieces, in which a comparatively large amount of material has to be removed, with a high degree of accuracy via the mechanical control axes. In the case of cutting tools having a diamond coating, these are e.g. PKD diamond coatings, the thicknesses of which are much greater than those of CD diamond coatings, and therefore the amount to be removed is correspondingly larger. Here, the production via the mechanical control axes for guiding the laser beam results in production periods which are only acceptable in exceptional cases.
EP 2314412 A2 describes a laser machining device for providing a blank with a contour, comprising a laser producing laser beam pulses, a deflection device which directs the laser beam pulses of the laser to predetermined impact points which are spaced apart from one another within a predetermined pulse area on the blank, and a positioning device which carries out a relative movement between the blank and the pulse area, wherein the relative movement proceeds in a relative movement direction along the edge and/or area to be produced.